Floating neutral

[Isetech]

What causes a floating neutral, When the neutral from a transformer, UPS or inverter does not have a neutral earth bond.

Examples of where you will find floating neutrals under normal operation conditions.

Transformers, where one of the secondary output terminals are not grounded.

low voltage control circuits.

Safety supplies.

Mobile Inverters.

Mobile Generators.

Mobile UPS.

Is it dangerous to have a floating neutral, that's the part that requires more discussion. Why, because in some cases it is important that the secondary side is not grounded, a pool safety transformer is a good example. It is regarded an isolated safety supply.

Should the output form a generator be grounded, if used as a mobile device, no. It it is connected to a fixed installation, yes.

Then we move onto the one that has many people very confused, the inverter.

Should the output of an inverter be grounded/bonded to earth, while operating under "normal" conditions, no, so why not, because the inverter uses the bond from the grid supply and therefore the ELU would function correctly and everyone would be happy. IF you bonded the earth/neutral while operating under "normal" conditions, it would create a second bond in the electrical installation (which is not allowed by law) and trip the ELU.

A standard mobile generator which in most cases would be a V-O-V (110-0-110 typical design for the USA), would have a floating neutral. However all the smart people in SA have decided that it is dangerous, so now they are saying the neutral (one terminal) output has to be grounded. The way I see it, the frame of the mobile generator could now end up with 230 volts to the frame, hence the reason for the V-O-V to make it safer 110 VAC.

By connecting the generator to a fixed installation, you would need to install a spike, bond the frame and created a bonded neutral/earth (so that it is no longer a floating neutral) at no point should generator be connected directly to the grid supply, hence the manual or auto changeover, unless it is designed for that application( to blend with the grid supply).

Then we move onto inline UPS systems which function online permanently (they dont switch over) they feed a clean pure sine wave to the supply, most commonly found in IT applications where a good clean stable power supply is required. As technology evolves, more device require a constant clean supply. So we fit all sorts of devices to attempt to reduce the failure of expensive electronic equipment now even in our homes.

Then you will find cheaper UPS devices, which in some cases have a very fast switching time so you would even notice because the computer would stay on. These mobile UPS units have a floating neutral. How would you know, by simply testing L-E and N-E, you will notice what seems like strange voltages between 80 and 120 VAC.

In the past a UPS would supply dedicated socket outlets (red sockets) which would not require earth leakage protection, so there was no need for earth/neutral bonding. We even had a dedicated earth stud for a "clean" earth which has since been scrapped.

[Isetech]

Then you have to ask yourself should it not be the manufacturers or supplier not familiarise themselves with the standards in that specific country and design the product to suit the country or at least offer a safe solution.

Selling products with international standards which dont apply to all the countries is where the fight should start.

If everyone is selling products with international standards, then every country should be working to the same standard and same system.

[GCE]

A standard mobile generator which in most cases would be a V-O-V (110-0-110 typical design for the USA), would have a floating neutral. However all the smart people in SA have decided that it is dangerous, so now they are saying the neutral (one terminal) output has to be grounded. The way I see it, the frame of the mobile generator could now end up with 230 volts to the frame, hence the reason for the V-O-V to make it safer 110 VAC.

.

If a genset is used on site it should be VOV for safety because of the 110v to earth vs 230V and is allowed as such.
On a fixed installation then it has to comply with grid specifications - SA grid is 230v with Neutral earthed at star point/start of supply .
Nothing confusing

In the past a UPS would supply dedicated socket outlets (red sockets) which would not require earth leakage protection, so there was no need for earth/neutral bonding.

That statement is incorrect on a number of levels - You still had to have neutral earth bond - If you dont have the bond a CB will not trip on an earth fault .
You would need to have tested polarity on sockets and loop impedance on an alternative supply - Neither of these tests would have past and therefore you could not have issued a COC

[Isetech]

It actually is a little confusing for many people, on one hand we are telling everyone that you shouldn't buy a V-O-V generators on the other hand we are saying you must buy a V-O-V generator for site.

What is even more concerning is that people are bonding the neutral and/earth on the generator.

In my case I use my "mobile" generator for site work and I connect it to my house using a 3 pin industrial plug. Its mounted on rubber wheels and it is still a V-O-V unit to make it safe while using on site.

If a genset is used on site it should be VOV for safety because of the 110v to earth vs 230V and is allowed as such.
On a fixed installation then it has to comply with grid specifications - SA grid is 230v with Neutral earthed at star point/start of supply .
Nothing confusing


That statement is incorrect on a number of levels - You still had to have neutral earth bond - If you dont have the bond a CB will not trip on an earth fault .
You would need to have tested polarity on sockets and loop impedance on an alternative supply - Neither of these tests would have past and therefore you could not have issued a COC

I have never seen a UPS with the neutral/earth bonded. I am sure there are places that do have a bond.

My 600 watt inverter wit the 12 VDC battery, that runs my TV, routers, CCTV and alarm systems has never had a bond, its a mobile unit that is on wheels on the floor. Its been like that since 2009. Because I have to replace the battery every 3-5 years, I dont bother fitting it back in the steel box.

[Derlyn]

It actually is a little confusing for many people, on one hand we are telling everyone that you shouldn't buy a V-O-V generators on the other hand we are saying you must buy a V-O-V generator for site.

What is even more concerning is that people are bonding the neutral and/earth on the generator.

In my case I use my "mobile" generator for site work and I connect it to my house using a 3 pin industrial plug. Its mounted on rubber wheels and it is still a V-O-V unit to make it safe while using on site.

There is a difference between a portable alternator and a standby alternator. 2 different things.
In fact there's a generator dealer in our valley who displays them separately. He must be the only one in the country who does so and he is the only one, as far as I'm concerned, who is doing it correctly.

In South Africa, a portable alternator is one that is VOV wound
A standby alternator is not VOV wound.

How does one get by 7.12.2.7 which says that a 230V generator with a VOV earth connection( centre tap on winding which is earthed ) shall not be connected to a fixed electrical installation? NOTE Such a generator may be used as a free-standing unit to provide power to specific appliances.

As an aside, I have noticed that over 90% of alternators 5KW and larger now offered for sale are not VOV wound.

I prefer calling them alternators seeing that they produce AC.

[Isetech]

There is a difference between a portable alternator and a standby alternator. 2 different things.
In fact there's a generator dealer in our valley who displays them separately. He must be the only one in the country who does so and he is the only one, as far as I'm concerned, who is doing it correctly.

In South Africa, a portable alternator is one that is VOV wound
A standby alternator is not VOV wound.

How does one get by 7.12.2.7 which says that a 230V generator with a VOV earth connection( centre tap on winding which is earthed ) shall not be connected to a fixed electrical installation? NOTE Such a generator may be used as a free-standing unit to provide power to specific appliances.

As an aside, I have noticed that over 90% of alternators 5KW and larger now offered for sale are not VOV wound.

I prefer calling them alternators seeing that they produce AC.

[Derlyn]

Hi All

Called out on Thursday for tenants shocking on taps.

We knew before we went to sight that the neutral was gone.

Sure enough. No Neutral.

While we were on sight the client asked if I knew a plumber, as there was a water leak.

I got up in the attic and found what had caused the leak.

Arcing between the hot water system and the tin roof. The pipe had arced through and was leaking.

Just shows how quickly a house can catch alight if the neutral decides to get stolen.

The photo is not as clear as daylight, but I'm sure you get the idea.

This photo was taken with the main switch turned off. Scary.